Author
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Rowe, Dennis |
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HILL, R - USDA, ARS (DECEASED) |
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Submitted to: North American Alfalfa Improvement Conference
Publication Type: Proceedings Publication Acceptance Date: 3/5/2000 Publication Date: N/A Citation: N/A Interpretive Summary: Plant breeding of alfalfa has been very successful, but our understanding of most of the important genetic processes has been inconsistent and fragmentary. The efficiency of different breeding methods has been the subject of many tests. A total of twenty-seven years of research by the authors using both "brute force" tests in field and greenhouse and theoretical investigations were reviewed. In publications, plant breeders usually focus much of their discussions on the significance of population improvement instead of failure in the selection attempts. For the private plant breeder, frequency of success and the rate of improvement are integral parts of personal success. Selection failures may have immediate effect on plant breeder's financial support and on his job security. A Review of selection success for seven diseases in several separate studies showed that selection was rarely effective more than 50% of the time. Experimental tests of best selection methods or procedures have resulted in few, if any, consistent results. The authors observe that most breeding research has been executed with minimal testing over environments and often used unrepresentative genetic materials. The authors proposed that the theoretical research, even with its simplifying assumption, has been more useful than all of the piecemeal applied studies in explaining or predicting selection gain and explaining what seem to be inconsistent responses. Plant breeders are encouraged to exploit the theoretical research to its fullest to improve their understanding and control of responses to selection. Technical Abstract: This is a review of solution oriented research on alfalfa improvement and the development of breeding theory executed by the authors on (1) selection responses, methods, and interpretations, (2) development of synthetic varieties, and (3) reality or accuracy of phenotypic measurements. In a series of experiments spanning a total of 27 years, tests were made in different populations with different traits comparing the gain with selection for intra-population improvement procedures and inter-population improvement procedures. Theoretical expected gains for all of these methods were developed and summarized in a single, terminal monograph. Other research showed the bias and distortions in selection caused by gametic disequilibrium found in the synthetic cultivars and crosses. Several experimental and theoretical studies showed the responses of replacing clones in a small synthetic variety and the effects of increasing gthe number of parents in the parental or Syn-O generation. Results suggested that general combining ability (GCA) was the single criteria for selection of best parents for the synthetic cultivar. Practical and theoretical research showed the difficulties of evaluating the GCA accurately. A major cumulative result of this research has been to show that breeding effectiveness on alfalfa has been extremely dependent on the populations and specific conditions of the evaluations and that selection gain is never a certainty. Also the theoretical research may have been more illuminating and useful than all of the field tests. |
